clean

src/board.rs

@@ -73,7 +73,8 @@ fn gen_adj_lookup() -> PosMap<ChainCollection> {
                     chains
                         .iter()
                         .flatten()
-                        .all(|(i, j)| (0..BOARD_SIZE).contains(i) && (0..BOARD_SIZE).contains(j)),
+                        .flat_map(|(i, j)| [i, j]) // flatten to just numbers
+                        .all(|x| (0..BOARD_SIZE).contains(x)),
                     "chains go out-of-bounds"
                 );
 
@@ -320,16 +321,15 @@ impl Board {
         ADJ_LOOKUP
             .get(i, j)
             .iter()
-            .filter_map(move |chain| {
-                let mut end_idx = None;
+            .flat_map(move |chain| {
                 for (idx, &(new_i, new_j)) in chain.into_iter().enumerate() {
                     let piece = self.get(new_i, new_j)?;
                     if piece == starting_color {
-                        end_idx = Some(idx);
-                        break;
+                        // SAFETY! get_unchecked is fine here because it's an index of itself, it's fine
+                        return Some(unsafe { chain.get_unchecked(..idx) });
                     }
                 }
-                end_idx.and_then(|idx| chain.get(..idx))
+                None
             })
             .flatten()
     }